a$.$ Find the average time $($in s$)$ required for an oxygen molecule to diffuse through a $0\mathrm{.}204$ mm thick tear layer on the cornea. $($Assume the diffusion constant of oxygen through tears is $1\mathrm{.}0{10}^{-9}\frac{m^2}{s}.)$

The average time is $$ s$.$

b$.$ How much time $($in $h)$ is required to diffuse $0\mathrm{.}54c{m}^3$ of oxygen to the cornea if its surface area is $1\mathrm{.}11c{m}^2?$

It takes $1357\mathrm{.}64$ x$.$